Guide
Before playing around with the build tool it may be best to consider what your intent or goal is for the build. I have a list of questions to consider which can considerably shape the choices you make for your build. Are you going into this to create a scape or is there a specific animal species you want to keep? If you establish this early on it will save you time later by avoiding choices that would not be compatible. You can start at any step in the build process. So for example if you have a particular fish species you want to keep you may want to start in the Stock step to select it and get some of the compatibility information to help guide what you select in your System step later.
Questions
The following questions can help guide you through fundamental decisions that drastically change what options you have to select from later. If you already know your goal/intent for this build then you likely already know the answer to these.
1. Saltwater or Freshwater
Saltwater
Saltwater has unique stocking that you cannot do in fresh, so your fish/snail/shrimp/etc. selections are different. You cannot do plants, but you get corals and macroalgae. The water is often more complex where you need salt initally and for water changes and RO to top it off due to evaporation. The equipment can differ, such as using skimmers rather than filters. As far as pricing salt tends to be more expensive.
Freshwater
Freshwater has unique stocking that you cannot do in salt, so your fish/snail/shrimp/etc. selections are different. You can use plants but not corals/macroalgae. Water is easier since you can typically use tap and add some declhorinator to it. Equipment is usually a bit easier and cheaper. Overall price is a bit cheaper than salt.
2. How big do you want to go?
The term "nano" does not have a clear meaning but I like to think of it as aquariums of size 30 gallons or less. What I also like about this is 30 gallons is a pretty good limit on what I think a single person could setup solo. Anything larger and you would likely need to involve a buddy to move it around. Smaller tanks can often be a bit harder to balance the water parametners compared to bigger tanks. As things get bigger however they get more expensive. More than that you may change how your system operates as you get bigger. Filtration is a good example of this. For freshwater tanks going from small to large, you would probably use an internal filter for small, then maybe a hang on back for medium, and as you get too big maybe a cannister or two. For saltwater it is a bit different since you kind of scale your sump and often just use as big a skimmer as you can fit. Maybe for small you use a hang-on-back skimmer (no sump), medium your tank has a built in sump (like an all-in-one system where it is in the tank) and you use an internal skimmer. For large you probably have a true sump that is plumbed, then you probably put however big of skimmer you can in there. If you are going to go the sump route, regardless fresh/salt, just know that unless its an all-in-one some plumbing would be required to get everything hooked up. If your tank is reef ready then it is already drilled, if not then you may have to drill yourself, or maybe use a hang-on-back overflow. So this question of "how big" is also kind of "how DIY" you want to go.
3. Reef or fish only
Reef
A reef tank is a saltwater tank with corals. Compared to fish only you will likely need higher lighting, higher flow, and higher filtration. Possibly even more stuff like dosing. Your fish selection will also be limited since some fish are not reef safe such as large angels, eels, file fish, groupers, puffers, trigger fish, and wrasse.
Fish only
There is a term called FOWLR which is "fish only with live rock". That is a common look for fish only tanks. You may not need as powerful equipment for lighting/flow. You should have access to more fish. This may be overall easier to maintain than reef.
4. Plants or fish only
This question is simliar to "reef or fish only" but more fish are compatible with plants than fish compatible with corals. I think your non-compatible fish are south american cichilds (african cichlids are a maybe), oscars, and plecos.
5. Aquarium or Paludarium
Aquarium
This site is currently focused on just aquariums.
Paludarium
I would have to perform more research here. Generally I think of these as partial filled aquariums and support creatures such as turtles, frogs, crabs, and more. Anything that needs a land part of their tank to get out of the water. Your plant selections may be a bit broader since you can have terrestial plants. I do not know of saltwater paludariums, but I think brackish ones exist, and might be popular to house mudskippers.
Build
Tank builds are broken down into three main steps or phases:
1. System
2. Scape
3. Stock
Eash phase can have dependencies on the others, so as you progress your build you may come across varying messages relating to compatibility.
The following is a summary for each phase.
System
The "System" phase refers to the hardware components of the build. This includes the tank, stand (optional), lighting, heating, filtration, and more. Those components are the primary ones, but depending on what you are going for can determine what all you will need. Most compatibility checks here are to ensure the components work sufficiently with each other such as enough heat/filtration for the volume of the tank, long enough light for the length, and so on.
Scape
The scape generally entails what goes into the tank minus the livestock. So this would commonly refer to the substrate, decorations (wood, rock, etc.), and plants (or perhaps coral and macroalgae for saltwater systems). Most compatibility checks here are for the plants, such as ensuring you have enough light to support them, the substrate has enough nutrients to support them, the tank is large enough, and so on. Petco has limited options for scaping but I will start there and perhaps expand into other online stores like modernaquarium later. Anything WYSIWYG would not be done through this tool. A good tool for simulating a scape is Scape It. Most plant info comes from tropica. Just a reminder that freshwater or saltwater you likely would need to cycle your tank after setup and scape for a while before adding stock.
Stock
Stock is the animals going into the tank. This is your fish, snails, shrimp, etc. This is where the bulk of the compatibility checks are performed. This helps ensure your selected fish are compatible with your system (tempature, filtration, volume), your scape (plant safe), and with each other (fin nipping or worse eating). Petco has a limited selection on their website but I will likely start there and expand later.
Stats
These are the stats that show in the right side panel.
IsFreshwater
This tracks your selection of freshwater vs saltwater. It can be used in conjunction with "Filter Stock pages by IsFreshwater" to filter Stock pages on their Environment property (Freshwater vs Marine). It also controls a few validations such as which compatibility chart is used (fresh vs salt) and how lighting is rated (plants vs corals).
Price
There are no validations tied to Price. This is totaled up from all the components. Price is expressed in USD.
Volume
Volume is used in several validations, mainly as a gate to ensure you have a non-zero volume before attempting a validation (like GPH). It is also used to calculate several stats, any that are "per gallon" for example. Volume comes from your Tank selection and sump selection. Volume is expressed in gallons.
FiltrationGPH
FiltrationGPH is your filtration (filter/pump) "Gallons Per Hour" and is a common metric used to describe the effectiveness of filters. It is additive based on your filter(s) and pump(s) selection. Typically you would either be using a filter or a sump-and-pump, but it will add regardless. There is one validation tied to this stat. This validation comes from thesprucepets.com. "The rule of thumb is that all the water in your tank should pass through the filter at least four times each hour."
Choosing the Right Size of Aquarium EquipmentFlowGPH
FlowGPH is your display tank flow (filter/pump plus powerhead) "Gallons Per Hour". It is additive based on your filter/pump and powerhead selection. There is one validation tied to this stat. It checks this value against your tank volume (not total volume in case you selected a sump). It only validates for saltwater.
How much Flow and How much Light | REEF2REEF Saltwater and ...DryWeight
This is the weight inside the tank based on the components selected. Currently there are 4 components that factor in to this: Tank, Substrate, Rock, and Wood. There is no validation related to this, it is just informational. This is measured in lbs.
WetWeight
This is the DryWeight plus the weight of water (water weight per gallon: 8.3454 lbs). There is one validation related to this to ensure the weight does not exceed the stand weight limit. This is measured in lbs.
TotalFishMaxLength
This is a measure of the total fish max length (MaxSize * Count * Quantity). There is no validation directly related to this stat, it is just informational. This is measured in inches.
TFMLPG
This "total fish max length per gallon" is my rough translation of the "1 inch of fish per gallon" guideline (freshwater). This is not a hard rule, just a guideline, and a lot of people prefer to not even consider it due to its flaws. However I still like knowing it so I am including it. Here is a relevant article from thesrpurcepets.com about it (Freshwater). I have another one included below for saltwater which is actually 1 inch of fish per 5 gallons.
Safe Stocking Guidelines for Aquariums How Many Fish Should I Put in My Saltwater Aquarium?HeaterWatts
This is the selected heaters WattageMax. This is measured in Watts. This is not validated directly, but is used within HWPG stat.
HWPG
"Heater Watts Per Gallon". There is just one validation related to this stat. This taken from thesprucepets.com.
Choosing the Right Size of Aquarium EquipmentSubstrateWeight
This is the total weight of the selected substrate. There is no validation directly related to this stat, but instead factors into SWPG. This is measured in lbs.
SWPG
"Substrate Weight Per Gallon". There is just one validation related to this stat. This validation only considers tank volume and not total volume (tank plus sump). This comes from thesprucepets.com. The first article is freshwater, second is saltwater, and I included a third for rock weight per gallon. We do not track a stat for rock weight per gallon but there is a validation.
Choosing the Right Size of Aquarium Equipment How to Use Live Sand in Your Saltwater Aquarium How to Work with Live Rock in a Marine AquariumEstLightRating
So this was rather complicated and I likely did not get it correct. It seems that there are many ways of evaluating your light performance, which results in an order of precedence on what metric you should use based on what data you have. PAR seems to be a great one (but even it could possibly be better with PPF and PPFD). Next would be Lumens, and last Wattage. So I try to evaluate PAR>Lumens>Wattage based on whatever data I have available. First I evaluate the light rating based on best available data, and then check each plant (or coral/algae/misc) LightDemand against it. The plant light demand comes from Tropica. Most of the plant data comes from Tropica. The coral/algae/misc data comes from LiveAquaria. The ranges for PAR/Lumen/Watt links are below. If your value is Unknown then it means you have something being calculated but it falls outside the ranges. If your value is N/A then it means you have not selected a Tank and Light yet or there is no data to use on the Light you selected. Also the volume used in calcs (Lumen/Watt) is the tank volume, not the total volume (tank plus sump). Another important note is that multiple lights are not additive. I assume in that case you are expanding your coverage area rather than increasing your light intensity.
PAR Lumen Watt How much Flow and How much Light | REEF2REEF Saltwater and ...EstFlowRating
This is evaluated according to the article linked below. It uses your FlowGPH and your tank Volume, not the total volume (tank plus sump). This is only applicable to Saltwater and gauges what corals/algae/misc can be supported in your tank.
How much Flow and How much Light | REEF2REEF Saltwater and ...EstTempRange
Measured in farenheit. This is the range of MinTemp to MaxTemp for the Stock selections. First the max min temp and min max temp is found across all Stock selections. Then each stock selection is evaluated against that range to see if it falls outside. Freshwater data comes from Aquadiction and Saltwater from LiveAquaria.
EstpHRange
This is the range of MinPH and MaxPH for the stock selections. First the max min pH and min max pH is found across all Stock selections. Then each Stock selection is evaluated against that range to see if it falls outside. Freshwater data comes from Aquadiction and Saltwater from LiveAquaria.
EstGHRange
This is the range of MinGH and MaxGH for the stock selections. Freshwater data comes from Aquadiction.
EstKHRange
This is the range of MinKH and MaxKH for the stock selections. Saltwater data comes from LiveAquaria.
EstSGRange
This is the range of MinSG and MaxSG for the stock selections. Saltwater data comes from LiveAquaria.
FreshCompChart
So this is not a Stat like the rest, but I wanted to have an explanation for the fish compatibility validations. I use the chart from Petco and I have a link to the pdf below.
Freshwater Compatibility ChartSaltCompChart
So this is not a Stat like the rest, but I wanted to have an explanation for the fish compatibility validations. I use the chart from Petco and I have a link to the pdf below.
Saltwater Compatibility Chart